1. Technical Field
The present invention relates to a liquid detecting unit and a liquid jetting device.
2. Related Art
In recent years, as an example of liquid jetting devices, inkjet printers are known. An inkjet printer can perform printing on a printing medium such as printing paper by discharging ink, as an example of liquid, from a print head onto the printing medium. Moreover, the inkjet printer is provided with an ink tank as a liquid container for storing ink, and performs printing by supplying the stored ink to the print head. As an inkjet printer of this type, one provided with a liquid detecting unit for detecting the residual amount of ink stored in an ink tank, which is one piece of ink information, is known (for example, see JP-A-3-275360).
There have been cases where in a liquid detecting unit, an electric current is caused to flow through ink in an ink tank in order to detect the ink residual amount. In this case, due to the ink being electrolyzed by the direct electrical current flowing therethrough, air bubbles can be generated, and the components of the ink can be deposited on an electrode. In this state, there has been a problem in that the air bubbles or the deposited components of the ink are mixed with the ink, are conveyed to a print head, and then clog the nozzle of the print head, thereby adversely influencing ink discharge. The liquid detecting unit in JP-A-3-275360 is provided with a voltage restriction unit, and a pulse voltage is applied between a plurality of electrodes. A means for accordingly detecting the ink residual amount while suppressing the electric energy to be applied and avoiding electrolysis is suggested. However, JP-A-3-275360 does not disclose a technical idea that the adverse influence due to electrolysis is avoided by causing an alternating electrical current to flow through the ink, including details of a means for the idea.
Note that an alternating electrical current is a current in which the polarity of a voltage applied between two electrodes periodically changes over time, and the direction of the current flowing between the two electrodes changes in accordance with the change in the voltage. The alternating electrical current is typified by a sine wave alternating electrical current. In this specification, an alternating electrical current including a sine wave alternating electrical current and a non-sine wave alternating electrical current is simply referred to as alternating current.